a. Field of the Invention
The instant invention is directed toward suspending, modifying, or controlling a medical procedure under certain conditions. More specifically, the instant invention relates to monitoring patient respiratory data and suspending, modifying, or controlling a medical procedure upon encountering an exceedance of at least one respiratory threshold.
b. Background
Cardiac mapping systems such as the Ensite™ Advanced Mapping System by St. Jude Medical, Inc., and the Carto™ Electroanatomical Mapping System by Biosense Webster provide non-fluoroscopic navigation of conventional electrophysiology catheters. The Ensite™ Advanced Mapping System's navigation methodology is based on the principle that when electrical current is applied across two surface electrodes, a voltage gradient is created along the axis between the electrodes. While any number of electrode pairs may be used, typically, six surface electrodes are placed on the body of the patient in three pairs: anterior to posterior, left to right lateral, and superior (neck) to inferior (left leg). The three electrode pairs form three orthogonal axes (X-Y-Z), with the patient's heart being at least generally at the center.
The noted surface electrode pairs are connected to the Ensite™ Advanced Mapping System, which alternately sends an electrical signal through each pair of surface electrodes to create a voltage gradient along each axis, forming a transthoracic electrical field. Conventional electrophysiology catheters may be connected to the Ensite™ Advanced Mapping System and advanced to the patient's heart. As a catheter enters the transthoracic field, each catheter electrode senses voltage, timed to the creation of the gradient along each axis. Using the sensed voltages compared to the voltage gradient on all three axes, EnSite™ NavX™ navigation and visualization technology calculates the three-dimensional position of each catheter electrode. The calculated position for the various electrodes occurs simultaneously and repeats many times per second (e.g., about 93 times per second).
The Ensite™ Advanced Mapping System displays the located electrodes as catheter bodies with real-time navigation. By tracking the position of the various catheters, EnSite™ NavX™ navigation and visualization technology provides non-fluoroscopic navigation, mapping, and creation of chamber models that are highly detailed and that have very accurate geometries. In the latter regard, the physician sweeps an appropriate catheter electrode across the heart chamber to outline the structures by relaying the signals to the computer system that then generates the 3-D model. This 3-D model may be utilized for any appropriate purpose, for instance to help the physician guide an ablation catheter to a heart location where treatment is desired/required.
In accordance with the foregoing, conventional electrophysiology catheter electrodes may be located in EnSite™ NavX™ navigation and visualization technology using a transthoracic impedance of a low-level signature frequency, which is sent and received between surface electrodes on the patient's skin. The calculated catheter electrode positions may be displayed relative to surface electrodes. These catheter electrodes may be used to mark discrete locations within the heart, such as for building models of cardiac chambers, marking discrete sites of diagnosis (mapping), or guiding and marking positions of therapy delivery.
It should be appreciated that during respiration portions of the thoracic cavity move relative to the surface electrodes and volumes may change. Thus, catheter electrodes in the heart move relative to the surface electrodes. Current systems do not account for this movement, and are accordingly creating static labeling of a dynamic model. This can cause errors in location, map generation and display, and treatment.
Current systems can try to correct for this artifactual motion by a respiration compensation functionality that is incorporated into the Ensite™ Advanced Mapping System. A respiration compensation functionality is utilized in the Ensite™ Advanced Mapping System to adjust to respiratory motion from intracardiac catheters by: (1) taking a 12-second data sample of patient respiration, including motion on intracardiac electrodes and impedance changes measured by the EnSite™ NavX™ navigation and visualization technology surface electrodes; and (2) following the collection of such a respiration data sample, the respiration compensation functionality may monitor the surface electrode impedance, and as the impedance changes, the respiration compensation functionality will adaptively compensate for motion artifacts on intracardiac electrode navigation. However, the respiration compensation functionality will only adapt to respiration levels (impedance levels) within the range measured during the sample. Respiration can also cause similar difficulties in systems that do no use surface electrodes.